As shown in FIG. 7, a glow plug 90 according to the background art has a rod-shaped ceramic heater 91, a cylindrical outer pipe 92, and a cylindrical metal shell 93. The ceramic heater 91 is held in the outer pipe 92 by tight fitting in the condition that a front end portion 91a and a rear end portion 91b of the ceramic heater 91 are protruded from the outer pipe 92. A front end portion of the metal shell 93 is bonded to an outer circumferential surface 92a of a rear end portion of the outer pipe 92. The ceramic heater 91 has a heating portion 912 in a front end portion 911a of a ceramic heater body 911. The heating portion 912 generates heat when electricity is applied to the ceramic heater 91. The ceramic heater body 911 extends in a direction of an axis O. The ceramic heater 91 further has a pair of lead portions 913 for current conduction. The pair of lead portions 913 are provided to extend from the heating portion 912 so that the pair of lead portions 913 are exposed to an outer circumferential surface of a rear end side 911b of the ceramic heater body 911. Application of electricity to the ceramic heater 91 is performed by a rod-shaped center pole 94 and a cylindrical member 95 in the following manner (e.g. see Patent Document 1). That is, the center pole 94 is located in the rear of the ceramic heater 91 in the direction of the axis O and extends in the direction of the axis so as to be electrically connected to the outside. The cylindrical member 95 has a front end portion 951 bonded to the outer circumferential surface of the rear end side 911b of the ceramic heater 91 by a wax material, and a rear end portion 952 bonded to an outer circumferential surface of a front end portion 94a of the center pole 94 by caulking so that one of the lead portions 913 is electrically connected to the center pole 94. As the material of the cylindrical member 95, a metal elastic material having elasticity such as stainless steel, copper, etc. is used in consideration of caulking, etc.
Patent Document 1: Japanese Patent Laid-Open No. 42671/1997 (FIG. 3)